The present invention relates to an electron multiplier having a micro-channel plate and to the application of the multiplier in radiation or particle detector devices.
When a micro-channel plate is introduced in a radiation or particle detector device, a certain number of difficulties are encountered. Said difficulties appear when, for example, an image intensifier tube of the proximity focus type is considered. Such a tube comprises generally an evacuated envelope which is closed by means of windows which are transparent to the light. Parallel to said windows there are a photocathode, a micro-channel plate and a fluorescent screen. Adequate electric potentials are applied to the various electrodes of the image intensifier. A problem to be solved relates to the uniformity of the interelectrode distance such that the spatial resolution of the amplified image is uniform. This problem is the more difficult to solve when the interelectrode distances are small, typically of a few tenths of a mm between the input face of the channel plate and the photocathode and 1.5 mm between the output face of the channel plate and the screen. If one succeeds easily to solve this type of difficulty when the diameter of the tube, hence that of the channel plate is medium, for example 2 to 3 cm, it is much more difficult to solve when the diameter is larger, for example of the order of 4 to 6 cm. It is difficult to avoid deformations of the micro-channel plate which occur as a result of thermal treatments to which it is subjected during the manufacturing process of the tube. Said deformations do not permit of maintaining a uniformity of the distances between the opposite faces of the channel plate and electrodes and hence also of the spatial resolution over the whole extent of the electrical field in the tube.
Another problem to be solved relates to the supply of electrical potentials to the metallized input face and output face of the channel plate. In prior art structures, the electrical potentials are generally applied to each face of the channel plate by means of metallic spring members resting on the periphery of the plate. During assembly, the use of such springs presents the disadvantage that, as a result of the pressure which they exert on the plate at the points of contact, grooves are often formed in the usually glass channel plate or even cracking or breaking of the plate may occur. Moreover, this type of contact is unsuitable in case the device in which the plate has been integrated would have to operate in the presence of severe vibrations. As a result of said vibrations there would be sliding of the plate on its contacts with abrasions of the metallizations and of the glass with the same consequences as those described previously.